Field of the Invention
This invention relates to bioresorbable implantable medical devices and methods of using such devices to stabilize or maintain an airway lumen during treatment of airway disorders.
Description of the State of the Art
This invention relates generally to treatment of laryngeal and tracheal stenosis with endoprostheses that are adapted to be implanted in the airway of an adult or child to stabilize or maintain the airway lumen. An “endoprosthesis” corresponds to an artificial device that is placed inside the body. “Stenosis” refers to a narrowing or constriction of a bodily passage or orifice. The endoprosthesis may stabilize or maintain the airway to facilitate restoring the airway lumen to a healthy or normal state and function. Laryngotracheal stenosis that is treatable by stenting has multiple causes. The most common factors for LTS are prolonged intubation usually associated with general anesthesia, external fracture of laryngeal, cricoid or tracheal cartilage structure, or subglottic stenosis. After surgical laryngeal reconstruction, a laryngotracheal stent is placed to stabilize the airway while it heals. The stent is temporary and the duration of stenting may be short on the order of 4-6 weeks, or longer than 2 months. The stent is not removed until the airway has sufficiently stabilized as premature removal can lead to airway collapse with resulting stenosis. Stabilizing an airway may correspond to permitting continuous unobstructed passage of air to the lungs. Airway disorders of various origins are treated with stents to stabilize or maintain the airway lumen. Stents, generally, are devices that hold open and sometimes expand a segment of an anatomical lumen such as an airway lumen, blood vessel, urinary tract, and bile ducts. A “lumen” refers to a cavity of a tubular structure. In addition to the conditions discussed below, any time the airway is opened to treat a disorder of the larynx, a stent can be considered for stabilization, scar prevention, or airway protection while the region heals.
Laryngotracheal stents, inserted after laryngotracheal reconstruction (LTR) to treat laryngotracheal stenosis, are most commonly used in children and young adults aged less than 20 years. Laryngotracheal stents are used in adults, primarily in the trachea, to relieve obstruction secondary to benign or malignant neoplasms.
Laryngotracheal stents are often used to keep the airway expanded after surgical reconstruction or trauma. Occasionally, laryngeal stents can be used for expansion of a diseased airway. Stenting in the tracheobronchial tree is usually used as a last resort for severe conditions such as recurrent carcinoma and severe tracheal collapse that results in periods of prolonged apnea.
The most common indication for laryngeal stenting follows reconstruction of laryngotracheal stenosis (LTS). Laryngeal stents can be used to keep the laryngeal lumen open and the reconstruction supported and stable. Occasionally, laryngeal stents are used following trauma to the larynx resulting in laryngeal fracture or injury. Stenting may help maintain lumen patency and prevent mucosal lacerations from forming obstructive scar tissue.
The first reason to use stents in cases of LTS is to support the larynx, after a reconstructive technique, often with some form of autologous cartilage, has been performed. A stent can be used to stabilize the cricoid plate once it has been divided anteriorly or posteriorly, with or without cartilage placement, to keep the complex in an expanded formation during healing. Stenting to help stabilize the laryngeal structure normally lasts for 2-6 weeks. It has been shown that when a cartilage graft is inserted, the minimum time necessary for a posterior cricoid split to heal in a distracted manner is 2 weeks. If stenting is performed for a shorter duration, the graft may prolapse into the lumen. For anterior graft placement only, stenting commonly lasts for a week or less.
The second reason for stent placement in LTS repair is to counteract scar contraction. Theoretically, this requires stenting for up to a 6-month period. In general, guidelines to determine the duration of stenting depend on the consistency of the stenosis, the anatomical distortion of the disease process, and the stability of the reconstructive areas.
Tracheal stenting may be used in the treatment of tracheal lesions, tracheomalacia, bronchomalacia, or stenosis that occurs following the resection of lesions.
The purpose of stenting for tracheal lesions varies from palliation, to cure, to stabilization while a reconstructive effort heals. Hence, the laryngotracheal stent primarily has a mechanical role. Use of the stent for delivery of a therapeutic agent is possible and useful agents to release would be antimicrobial agents to combat infection, antiproliferative agents to reduce obstructive scarring, and agents to promote healing. In adults, primary cancer of the tracheobronchial tree or cancer from the head, neck, or chest that extends into the tracheobronchial tree frequently causes lumen compromise and airway obstruction. The intraluminal component can be removed with laser treatment, mechanical debulking, electrocautery, brachytherapy, photodynamic therapy, or cryotherapy. A stent can then be placed to maintain the airway lumen following debridement to counteract collapse or edema. Alternatively, stents can be placed that help compress any lesion extending into the trachea or bronchi, without the need for debulking.
Stents have been used successfully to palliate patients with inoperable bronchogenic cancer, primary tracheal tumors, and metastatic malignancies. Placing a stent in a patient with a terminal illness allows that patient to breathe comfortably and prevents death from asphyxiation.
Tracheomalacia and bronchomalacia (sometimes called tracheobronchomalacia) may be primary or secondary in nature. These conditions usually occur in children, but they can be observed in adults. Tracheomalacia and bronchomalacia are termed primary if they arise from primary cartilage abnormalities of the trachea, such as immature formation of the cartilaginous rings in neonates or relapsing polychondritis in children and adults. Primary tracheomalacia is often observed with a tracheoesophageal fistula. Secondary tracheomalacia or bronchomalacia is caused by extrinsic compression from a structure in the mediastinum.
If tracheomalacia or stenosis occurs following the resection of lesions, stents can be placed in the trachea to prevent scarring or to provide support for the operated segment while it heals. In most situations, surgical correction as primary treatment for a disease process is preferred to stenting alone because complications are decreased. However, situations arise in which patients cannot undergo formal corrective surgery, and stent placement is the only way to prevent a severe apneic event or death.
Current laryngotracheal stents are durable devices, made of silicone, poly(tetrafluoroethylene) (PTFE, Teflon), or other polymers. These devices are removed after implant times ranging from 4 weeks to several months. FIGS. 1A-C depict commonly used devices, including the Montgomery stent, Montgomery T-tube and Aboulker stent, respectively.
If the stenosis is confined to the larynx (i.e., glottis, subglottis), stenting can be short- or long-term. Short-term stenting may be defined as stenting for less than 6 weeks. Long-term stenting is defined as stenting for more than 6 weeks.
Short term stenting for 6 weeks or less may be used because granulation tissue forms at the lower end of the stent above the tracheotomy, potentially leading to tracheal stenosis or collapse above the tracheotomy site. Short-term stenting may also be used for stabilization of cartilage grafts following LTR and/or for separation of mucosal surfaces during healing following laryngeal trauma, repair of web formation or atresia, or excision of a laryngeal lesion. Stents for these indications include Aboulker stents, silicone stents, Montgomery laryngeal stents, endotracheal tubes, and laryngeal keels.
In FIG. 1C, the representative (non-inclusive) samples demonstrate various sizes of Aboulker stents, ranging from 15 mm in diameter at the top to 3 mm in diameter at the bottom. These stents are hollow and are coated with PTFE.
The Montgomery Laryngeal Stent is a molded silicone prosthesis designed to conform to the normal endolaryngeal surface and is constructed of radiopaque implant grade silicone that is firm enough to support the endolarynx postoperatively, yet is soft and flexible enough to ensure a conforming fit while minimizing injury to soft tissues.
The Montgomery T-Tube is designed to maintain an adequate airway as well as to provide support in the stenotic trachea that has been reconstituted or reconstructed.
Use of durable stents usually requires removal of the stent after allowing a period of time for healing to take place. These devices have several complications including migration, fracture, keloid formation, granulation formation, and infection.
Inspection of FIGS. 1A-C reveals they are simple devices that are not expanded in place, are not fenestrated and have various levels of flexibility and compliance. As can be seen in FIG. 1AC, these devices come in a variety of sizes to match different anatomies and this is particularly driven by pediatric use. These devices are all inserted at the as-fabricated or final diameters and are not expanded once inserted in an airway.
Another challenge with these durable stents is selecting how long to keep them in place. LTR requires anterior and/or posterior cricoid splits, sometimes combined with cartilage tissue grafts. After the procedure, the stent is put into place to hold open the airway while healing occurs. The stent can also increase the stability of a graft and prevent scar contracture. Premature removal of the stent can lead to LTR failure.